A major goal of research proposal is to establish the mechanism by which the expression of G-protein-linked receptors (GPLRs) are regulated in normal and disease states, employing the beta-adrenergic receptor (beta2 AR) as the prototype for this class of more than 300 receptors. I propose to explore a feature common to many members of the superfamily of GPLR, i.e., agonist-induced down-regulation of receptors. Most studies to date have focused only on short-term mechanisms of desensitization. Those mechanisms include post-translational protein modification such as phosphorylation, interactions with regulatory proteins such as arrestins and receptors kinases, and physical sequestration of the receptor away from other signaling components Despite intense interest in the mechanisms which regulate short-term desensitization, very little is known about the long term regulation of receptor function. One mechanism through which a receptor can be regulated by is by altering its level of expression. This could occur through changes in the rate of protein degradation, recycling, protein synthesis, or through changes in the rate of synthesis of degradation of mRNAs encoding the receptors. My work over the last six years as focused on the latter control mechanism. We have identified, characterized a purified a 35,000 Mr protein (betaARB=betaAR mRNA-binding protein). This protein is induced by beta-adrenergic agonists and binds to beta2-receptor mRNAs that display agonist-induced destabilization. The expression level of this protein, identified by UV-cross-linked label transfer varies inversely with receptor mRNA. This protein appears to be involved in a very novel regulatory pathway in that it appears to destabilize the receptor mRNA. My specific aims for this proposal are as follows: #1) To obtain sequence information and raise antibody for the purified betaARB protein and use these information to molecular clone the full length cDNA for betaARB protein. #2) To study the mechanisms by which betaAR5B protein participates in beta2AR mRNA degradation and characterize the intracellular properties of this polypeptide.